BACKGROUND: Disease-modifying treatments (DMTs) for multiple sclerosis (MS) are associated with causing an increased risk of infection. However, MS patients have an increased risk of mild and severe infections in the absence of DMT, which may be related to MS disease progression. Information on the dynamics of infection incidence in the MS population can help to disentangle the effects of DMTs from background MS prognosis.
OBJECTIVES: To examine over the past two decades the rates of infections in MS patients before and after MS diagnosis by patient subgroup.
METHODS: A retrospective cohort study was conducted in the UK Clinical Practice Research Datalink (CPRD) Gold. 7219 patients diagnosed with MS were included from January 2003 to November 2019. Each MS patient was matched approximately 1:2 to patients from the general CPRD population by birth year, sex, practice and calendar year. Incidence rates per person year (IR) of urinary tract infection (UTI), skin and subcutaneous tissue infection, sepsis, respiratory infection, and gastrointestinal infection were calculated per study year. The average change in infection rate 5 years after patients' MS diagnosis compared to 5 years before was calculated across the whole study and per year. Analyses were stratified by age at diagnosis, sex, number of infections within 12 months prior to cohort entry and whether the first recorded MS diagnosis was before or after 2003. All analyses will be replicated in a larger CPRD Aurum cohort (13752 MS patients).
RESULTS: The incidence rate of infections in MS patients was 1.9 times higher than the general population over the study period (MS: 0.53 [0.52-0.53] vs non-MS: 0.28 [0.27-0.28], with UTIs most frequent (MS: 0.19 [0.19-0.20], non-MS: 0.056 [0.055-0.058]). A higher infection rate was found in CPRD Aurum (MS, any infection IR: 0.62 [0.62-0.63]). Infection rates were higher in women than men (0.59 [0.58-0.60], 0.36 [0.35-0.37], respectively). The incidence of infections was on average 30 percent higher within 5 years after MS diagnosis (IR 0.45, 95% CI 0.44-0.46) than the 5 years before (IR 0.35, 95% CI 0.34-0.35). The infection rates and differences in infection rate pre- and post-diagnosis declined over the study period across the subgroups. Full analyses in CPRD Aurum will be presented at the conference.
CONCLUSIONS: The rates of five key types of infection decreased between 2003 and 2018, but remained higher than in the general population. Consideration of patient characteristics associated with the risk of infection may be valuable for disease management decisions in MS.
